Effects of rapid maxillary expansion on the midpalatal suture a systematic review

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Systematic review
Effects of rapid maxillary expansion on the 
midpalatal suture: a systematic review
ShiYao Liu, TianMin Xu and Wei Zou
Department of Orthodontics, School and Hospital of Stomatology, Peking University, Beijing, China
Correspondence to: TianMin Xu, Department of Orthodontics, School and Hospital of Stomatology, Peking University, #22 
Zhongguancun South Avenue, Haidian District, Beijing 100081, China. E-mail: tmxuortho@163.com
Summary
Objective: To identify and qualify the scientific evidence on the immediate and long-term effects 
of rapid maxillary expansion on the midpalatal suture in growing teenage or young adults, the 
related articles were selected.
Materials and methods: Literatures were searched in the electronic databases, including Medline, 
Embase, Web of Science, and Cochrane Library. A methodologic-quality scoring (13-point) scale 
was used to evaluate the quality of the studies.
Results: Twelve relevant articles were identified. Midpalatal suture opening during orthodontic 
treatment with rapid maxillary expansion (RME) amounted to 12–52.5 percent of the total screw 
expansion. After the treatment of RME, the midpalatal suture seemed to be recalcificated, so the 
expansion of the midpalatal suture was stable, but there was no consistent evidence on whether 
the midpalatal sutural opening was parallel or triangular.
Limitations: The methodologic quality of the included studies was assessed rigorously and many 
deficiencies were found.
Conclusions: The majority of the articles were judged to be of low quality. Therefore, we could not 
draw any accurate conclusion on the basis of evidence in this systematic review.
Introduction
The most effective orthopedic treatment that aims to increase the 
maxillary transverse width is rapid maxillary expansion (RME) 
(1). It has also been recognized as a safe and reliable orthopedic 
procedure.
The first use of RME was described by Angell (2) in 1860. Total 
expansion from RME has three parts: midpalatal suture expansion, 
alveolar expansion, and dental tipping.
Previous reports on RME skeletal and dental effects are contra-
dictory because of variable study designs, sample sizes, and research 
approaches. Two meta-analyses regarding the transverse dental 
effects of RME have been published (3, 4). One systematic review (5) 
about the long-term dental effects of RME has been published. Two 
systematic reviews (6, 7) partly about the immediate skeletal effects 
of RME have been published but to date there are no systematic 
reviews specially regarding immediate and long-term skeletal effects 
on the midpalatal suture.
The objective of this article was to assess the evidence on the 
amount of midpalatal suture opening and the long-term skeletal 
effects on the midpalatal suture.
Materials and methods
Selection criteria
Two investigators selected articles according to the selection criteria. 
The inclusion criteria were as follows:
Studies of human clinical trials, published in English.
Studies on healthy children or young adults who had maxillary transverse dis-
crepancy or upper dental arch constriction, such as unilateral or bilateral pos-
terior crossbite, some crowding, and so on, and needed maxillary expansion.
Studies that included clear descriptions of the type of appliances applied.
Prospective and retrospective original studies with a minimum of five subjects 
in the study sample.
During the evaluation period, no surgical or other treatment in progress that 
would influence the RME therapy.
European Journal of Orthodontics, 2015, 651–655
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Studies that concern human subjects with quantitative data on the immediate 
effect of RME assessed by cone-beam computed tomography (CBCT) or 
computed tomography (CT) or occlusal radiographs.
The exclusion criteria included studies concerning merely the slow 
palatal expansion, cleft lip and/or palate or other craniofacial syn-
drome diagnosis, surgically assisted expansion, functional appliance 
therapy, and protraction headgear or facemask therapy, and case 
reports.
Search methods
Medline (from 1966 to June 2014), Embase (from 1988 to June 
2014), Web of Science (from 1945 to June 2014), and Cochrane 
Library (from 1945 to June 2014) databases were searched, and so 
were the reference lists of selected articles, which may have been 
missed in the databases. Two review authors searched the databases 
independently and disagreements were settled through discussion. 
The search strategy is shown in Supplementary Table I.
The flow diagram is shown in Figure 1.
Data extraction and analysis
Articles that seemed to meet the selection criteria on the basis of the 
title and abstracts were selected. If not enough relevant information 
was provided in the abstract, the full text would be obtained. The 
two searchers settled discrepancies through discussion (interexam-
iner κ = 0.900).
The final selection was completed by reading the complete arti-
cles independently. The selection criterion was used again to make 
the final decision. We still reach a consensus by discussion in cases 
of any discrepancies (interexaminer κ = 0.985). Once specific data 
were necessary but not stated in the article, we would make efforts 
to contact the author to obtain the additional information needed.
Finally, 12 articles that met the selection criteria remained. 
Information on the following items was gathered: study country, 
design, the size, gender, and age of the participants intervention 
type, rate of screw activation (mm/day), endpoints, retention time, 
imaging parameters such as type, measurements, outcome measure, 
the amount of midpalatal suture opening (mm), midpalatal suture 
opening parallel or triangular, the post-retention effects of rapid 
maxillary expansion, and the percent of midpalatal suture opening 
amounted to the total screw activation.
According to the PRISMA (Preferred Reporting Items for 
Systematic Reviews and Meta-Analyses) statement, in the design 
or conduct of a study, the defects may produce bias, so the assess-
ment of methodological quality for this study gives an indication 
of the strength of evidence. However, no specific approach for 
evaluating methodological quality can be applied to all systematic 
reviews (8, 9).
In our study, a 13-point scale was used to assess the quality of 
the articles, which was developed after the study of Lione et al. (6) 
by analyzing the following characteristics: description of selection 
process, study design (retrospective, prospective, or randomized), 
Figure 1. Study flow diagram. From Moher et al. (8).
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consecutive cases, sample size, choice of outcome measure, adequacy 
of method error analysis, adequacy of statistical analysis, and power 
of the study. The quality of the studies was evaluated in Table 1 and 
Supplementary Table II. The same two researchers scored each study 
and discrepancies were resolved through discussion and negotiation.
Statistical analysis
A meta-analysis of the results of the studies was planned, so the 
assessment of heterogeneity of the studies was made by calculating 
the I2 index. However, the heterogeneity is too high (I2 > 75 percent) 
to make a meta-analysis, which might lead to misleading results. As 
a result, a systematic review was considered. By collecting, apprais-
ing, and synthesizing the evidence from scientificstudies, systematic 
reviews make a comprehensive summary of the available evidence, 
so as to provide answers to scientific questions (10).
Results
Medline yielded 290 publications; Embase, 520 publications; Web 
of Science, 768 publications; Cochrane Library, 8 publications. In 
addition, 15 records were identified through hand/manual search. 
Application of the inclusion and exclusion criteria identified 12 rel-
evant publications finally.
Six studies (12–17) were prospective, and three studies (19, 21, 
22) were prospective and randomized. One study (11) was a ran-
domized controlled trial, and the other two (18, 20) studies were 
unreported.
The average age at the beginning of orthopedic expansion in the 
samples was ranging from 7 to 15 years. As a whole, in 10 studies 
(11–16, 18, 20–22), the sample comprised teenagers; in two studies 
(17, 19), the sample was older than 15 years.
The devices applied were Hass expanders, which were bonded 
with acrylic coverage on the occlusal surface of posterior upper 
teeth, or hyrax expanders, which were banded with the two or four 
anchored tooth.
The methods used to detect the treatment effects were different: 
two studies (19, 22) used 2D radiographic techniques, and the other 
10 studies used 3D radiographic techniques.
The screw was activated 0.5 mm/day in five studies (14–17, 22), 
0.8 mm/day initially, then 0.4 mm/day in one study (11).
Four studies (12, 17, 19, 22) used a clinical evaluation. Four 
investigations (14–16, 21) reported that the required expansion cor-
responded to a precise amount of screw expansion of 7 mm. Two 
investigations (11, 13) reported that the required expansion corre-
sponded to an amount of screw expansion of 8 and 8.19 mm. Two 
investigations (18, 20) unreported the amount of screw expansion.
Immediate changes of midpalatal suture
Measurements of changes in midpalatal suture width during RME 
were presented in all of the included studies.
Six of them presented data for both the anterior and posterior 
regions. The mean expansion changes in the anterior midpalatal 
suture in the region ranged from 2.42 to 4 mm, which corresponded 
to 34.6–50 percent of the total screw expansion. Mean expansion 
changes in the posterior midpalatal suture ranged from 0.84 to 
2.88 mm, corresponding to 12–36 percent of total screw expansion. 
Five of them presented data for Sut3-3 and Sut6-6 width. The mean 
expansion changes between the 3-3 midpalatal suture ranged from 
1.52 to 4.3 mm, which corresponded to 21.7–52.5 percent of the 
total screw expansion. Mean expansion changes in the 6-6 midpala-
tal suture ranged from 1.6 to 4.3 mm, corresponding to 22.9–52.5 
percent of total screw expansion.
Long-term changes of midpalatal suture
Nine studies (11, 14–17, 19, 21, 22) analyzed the long-term effects 
of RME. After RME therapy, the device was maintained as a passive 
retainer for a minimum of 3 months and a maximum of 12 months. 
Long-term changes of midpalatal suture after maxillary expansion 
were not significant, so the opening of the midpalatal suture was 
stable.
Four studies (11, 12, 15, 19) concluded that the suture opened 
in a triangular shape, of which the largest opening was at the ante-
rior region. Two studies (13, 14) reported that the midpalatal suture 
opening was parallel.
The reviewed articles had different endpoints and different refer-
ence points when measuring the midpalatal suture opening, which 
makes comparisons difficult.
Quality analysis
A quality analysis of the 12 retrieved studies was accomplished 
according to the criteria in Table  1. Interexaminer agreement for 
the quality assessment was 0.95 (kappa statistics). The judged qual-
ity and methodologic soundness for the 12 selected studies are 
presented in Supplementary Table II. Two studies (11, 21) were of 
medium high quality, four studies (13–15, 19) were of medium qual-
ity, and the other six (12, 16–18, 20, 22) were of low quality.
Discussion
This review is the first systematic review to evaluate the immediate 
and long-term midpalatal suture response to RME treatment.
Age
The impact of age on skeletal effects of RME is an interesting issue in 
the clinical situation. Generally speaking, the expansion through the 
opening of the palatal suture progressively becomes more difficult as 
the patients grow old.
The age range in the articles reviewed was 5–20 years. In two 
studies (17, 19), the sample was older than 18 years, but the midpal-
ate suture was still separated.
In a study by Korbmacher et al. (23), human-palate specimens 
from individuals aged 14–71 using CT were assigned to three 
age groups (<25, 25 to <30, and ≥30  years). Significant differ-
ences between age groups were only found for bone density. The 
Table 1. Quality assessment
Study Study design Judged quality standard
Weissheimer et al. (11) Prospective Medium high
Ghoneima et al. (12) Prospective Low
Christie et al. (13) Retrospective Medium
Ballanti et al. (14) Retrospective Medium
Lione et al. (15) Retrospective Medium
Podesser et al. (16) Retrospective Low
Baydas et al. (17) Prospective Low
da Silva Filho et al. (18) Retrospective Low
Davidovitch et al. (19) Prospective 
randomized
Medium
da Silva Filho et al. (20) Retrospective Low
Garib et al. (21) Prospective 
randomized
Medium high
Lamparski et al. (22) Prospective 
randomized
Low
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middle-aged group exhibited the highest bone density (53.2 percent), 
while it was significantly lower in the youngest and the oldest age 
groups. Neither the mean obliteration index nor the extent of inter-
digitation correlated with chronological age. Therefore, sutural bone 
density seems to be the parameter limiting conservative RME.
Device
There are a variety of expanding devices applying to rapid maxil-
lary expansion. The type of appliances were expanders that attached 
primarily to the posterior teeth in all of the included studies and 
exerted pressure on the hard palate in half of the studies (Haas-type 
expanders).
Regardless of the type of expanding devices, RME is an effective 
procedure that is able to produce transverse skeletal effects on the 
maxilla by opening the midpalatal suture.
Computed tomography/cone-beam computed 
tomography
In contrast to the 2D imaging, if the structural overlap is the main issue 
in the diagnostics, the use of the low-dose CT/CBCT imaging can be 
justified for gathering the most adequate information for the treatment. 
Thanks to CT/CBCT technology, it allows clinicians and researchers to 
make a quantitative evaluation for the bone changes in three dimensions.
However, the radiation dosage and its bearing on growing 
patients must be kept in mind. Even though CT imaging may be 
available, regular use of it for orthodontic or dental care may not 
be justified.
Rate of screw activation (mm/day) and endpoints
In this study, we found that the midpalatal suture opening was not 
closely associated with the rate of appliance activation, but with the 
amount that the appliance is expanded, which means the endpoints 
and probably the amount of residual load remaining at the termina-
tion of appliance activation.
Retention time
The study by Krebs et al. (24) with metallic implants has shown that 
the expansion of the suture itself is very stable after retention for 
3 months but that the unavoidable buccal tipping of premolars and 
molars was followed by an uprighting for a long time. In the study of 
Ekström et al. (25), after 3 months, the process of mineralization has 
become fairly well established in the expanded suture.
Not only the formation of the midpalatal suture itself but also 
the establishment of a stable relationship at the articulations of the 
maxilla and other bones of the facial skeletonwould determine the 
retention time of RME.
Furthermore, it seems that the length of time needed for the skel-
etal readjustment during retention depended on the amount of resid-
ual load remaining at the termination of appliance activation (26).
Immediate changes of midpalatal suture
Midpalatal suture opening during orthodontic treatment with RME 
amounted to 12–52.5 percent of the total screw expansion, which is 
consistent with the result of previous research (20–50 percent) (7).
Long-term changes of midpalatal suture
Long-term changes of midpalatal suture after maxillary expansion 
were not significant, which indicated that the change of the midpala-
tal suture was stable.
In the study of Davidovitch et al. (19), due to 1 year after RPE 
therapy, the anterior midpalatal suture lost up to 27.5–46.38 percent 
with the two-band hyrax appliance, while it lost up to 58.87–75 
percent with the four-band. The posterior midpalatal suture lost up 
to 100 percent with the two-band, while it did 73.71 percent with 
the four-band. Ballanti et  al. (14) believed that after the 6-month 
retention period, the midpalatal suture appeared reorganized with 
a transverse dimension similar to the pre-treatment width. The mid-
palatal suture lost up to 89.55 and 77.78 percent of its increased 
area at anterior nasal spine and posterior nasal spine, respectively. 
However, these results did not exclude the growth factor.
Limitations
The methodologic quality of the included studies was assessed rigor-
ously and many deficiencies were found. None of the selected studies 
were of high value of evidence, and only one randomized controlled 
trial was identified. Most significant deficiency was the lack of char-
acterization of power of the study, consecutive cases, and sample 
size. Only one study (14) used power of the study.
Therefore, it might be sound to interpret the results from these 
studies with caution.
Conclusions
The aim of this systematic review was to find out about the opening 
of the midpalatal suture and the long-term effects on the midpalatal 
suture. After assessing the quality of the retrieved articles, it may be 
concluded that these questions cannot be fully answered.
1. Heterogeneity of the studies was too high (I2 > 75 percent), so a 
meta-analysis was not used.
2. RME is an effective procedure that is able to produce transverse 
skeletal effects on the maxilla by opening the midpalatal suture 
regardless of the type of palatal expander.
3. Midpalatal suture opening during orthodontic treatment with RME 
amounted to 12–52.5 percent of the total screw expansion. After 
RME, the suture seemed to be reorganized, so the expansion of the 
midpalatal suture was stable, but there was no consistent evidence 
on whether the midpalatal sutural opening was parallel or triangular.
4. The quality level of the studies was not sufficient enough to draw 
any accurate conclusion on the basis of evidence. Additional rand-
omized controlled trials with sufficient power are required to add 
further insight into the 3D effects of RME on midpalate suture.
Supplementary material
Supplementary material is available at European Journal of 
Orthodontics online.
Funding
The work was supported by National Natural Science Foundation of 
China (No. NSFC81371192).
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